THIS INVENTION relates to electrode assemblies for use in thermal plasma generating devices and, more particularly, to electrode assemblies of the type comprising a central water-cooled electrode surrounded by a sheath which, together with the electrode, defines an annular passage for the necessary gas to be ionised to form the plasma.
Generally such outer sheaths are also of a water cooled nature and are made of metal. These electrode assembles have associated therewith various problems, one of which is the problem of starting or striking the arc initially between the co-operating electrodes of opposite polarity. As a result of the fact that the one electrode is often a bath of molten slag or metal it is usually not possible for the other electrode to touch same in order to make initial electrical contact. These problems often result in damage to the electrode assemblies.
A further problem associated with such water cooled electrode assemblies is that, as a result of the fact that the sheath generally approaches the potential of the electrode, stray arcing onto the sheath can occur thereby damaging the sheath and ultimately the entire electrode assembly.
It is an object of this invention to provide an electrode assembly for use in thermal plasma generating devices which is easier to use for the purpose of initiating an arc preparatory to plasma generation and which, by its very nature, protects the electrode against stray arcing. The electrode assembly provided by this invention has, in addition, a variety of advantages which will be outlined below.
In this specification the term "high melting point" when applied to a material is intended to mean a material which has suitable high temperature properties, that is to say it does not melt or sublime below 2000.degree. C. It will be noted that this term extends to materials which may sublime instead of melting.